On the night of the North Korean invasion, Truman convened the first Blair House Meeting of his closest advisors. Though the meeting did not focus solely on Korea, in fact it began with a discussion of the US policy toward the Nationalist Chinese in Formosa (an issue MacArthur believed to be of great importance) Truman allowed Dean Acheson to speak regarding the Korean situation. Gen. Omar Bradley summarized the group's feelings, saying that the US would have to "draw the line" somewhere, and that Korea seemed as good a place as any. The immediate results of the Blair House Meeting were orders to evacuate American civilians from Korea, to provide military supplies to the embattled South Korean army, and to move the 7TH US Fleet into the Formosa strait, blocking the People's Republic of China from invading Formosa while the US was distracted with Korea.
MacArthur's reports grew worse over the next few days, describing the North Korean rout of ROK forces. The ROK army fled south, to the tip of the peninsula, in the direction of the port city of Pusan. On June 27, 1950 the US promised naval and air support to South Korea. Truman further hoped to discourage the Soviets or the Chinese Communists from getting involved in the war by integrating US troops into a force from the UN, and claiming the whole operation to be UN sanctioned and led.
Fleeing across the Han River Bridge, the panicky South Koreans blew the bridge before all the fleeing South Korean soldiers could get across. Hundreds died, and men and equipment were stranded on the other side. Major-General John H. Clark and ROK chief-of-staff General Chae Byong Duk consolidated what remained of their forces to establish a headquarters at Suwon. In a personally dangerous move, MacArthur flew in to Suwon and drove up to the front to see the fighting for himself. Based on his trip to the front, MacArthur cabled Washington for authority to commit ground troops. Calling his decision a "police action", Truman allowed MacArthur to move a US regiment to Pusan. Truman did not, however, immediately send to Korea the number of troops MacArthur wanted.
On June 30, with the ROK army in dire straits, Truman relented and gave MacArthur authorization to transfer 2 full divisions from Japan to Korea. For roughly two-and-a-half months, MacArthur simply tried to prevent the North Korean army from taking Pusan. Meanwhile, the US conducted a strategic bombing campaign and blockaded the coastline with warships. While Navy and Air power had little effect, MacArthur did manage to attain his main goal of holding Pusan. Also, during this delay, MacArthur was able to transform his out-of- shape occupation force into an army.
By July 4, 1950, the balance had begun to swing toward the US. On July 7, the UN asked the US to appoint a UN commander. Truman quickly made MacArthur Commander in Chief of the UN Command (CINCUNC). MacArthur responded to this honor by demanding more troops. It was not log before Truman's Korean War budget neared the tripling of military expenditures recommended by NSC- 68.
Trapped, backed into a corner against the sea, the situation continued to look bleak for the US/UN/ROK forces in South Korea. UN ground troops, under Lt.- general Walton H. Walker, commander of the UN ground troops in Korea, spent the bulk of their time working hard to build the "Pusan Perimeter", a fortress- like series of entrenchments in southeastern Korea. Still, these entrenchments offered little chance for US/UN/ROK counteroffensive. The anti-communist forces seemed stuck.